Who is Participating?

You might as well just add this user to the "LOCAL ADMINS" group. If you give a user write permission to the HKEY_LOCAL_MACHINE portion of the registy, then they can obtain administrator access anyway.

But if you must, open REGEDT32 and modify the permissions on the HKEY_LOCAL_MACHINE hive to permit the user to have full access. Note that you must use REGEDT32 and NOT REGEDIT. REGEDIT has no ACL modification capabilities.